trigger billLiveOpportunityTrigger on Opportunity (after update) 
{
    List<Fulfillment_Task__c> tasks = new List<Fulfillment_Task__c>();
    
    ID billingRTId = RecordTypeHelper.GetRecordTypeID('Fulfillment_Task__c', 'Billing'); 

    for(Opportunity opp : Trigger.new) 
    {       
          if((opp.StageName == 'Contract - Live') && 
          (opp.StageName !=  System.Trigger.oldMap.get(opp.Id).StageName))
        {
            Fulfillment_Task__c task = new Fulfillment_Task__c();
                        
            task.RecordTypeId = billingRTId;
            task.Opportunity__c = opp.Id;
            tasks.add(task);
        }       
    }
    
    insert tasks;
}